626 
ENGINES. 
cold water to touch it ; and by protecting it 
from the air or other cold bodies, by a sur- 
rounding case tilled with the steam, or with 
hot air or water, and by coating it over with 
substances that transmit heat slowly. He 
makes his vacuum to approach nearly to that 
of the barometer, by condensing the steam in 
a separate vessel, called the condenser; 
which may be cooled at pleasure without 
cooling the cylinder, either by injection of 
cold water, or by surrounding the condenser 
with it ; and generally by both. He ex- 
tracts the injection-water and detached air 
from the cylinder or condenser, by pumps, 
which are wrought by the engine itself ; or 
he blows it out by the steam. 
As the inside of the cylinder was in the 
old engine exposed to the air at every stroke 
when the piston descended, and was consider- 
ably cooled thereby, he incloses the top of 
the cylinder by a metal plate, having a hole 
in it, through which the piston-rod works in 
a collar of leathers ; and instead of employ- 
ing the pressure of the atmosphere to force 
down the piston, he introduces the steam 
above the piston, when the vacuum is formed 
underneath, and employs it to produce this 
effect: thus making the direct pressure of 
the steam the moving power, as in the ori- 
ginal construction of the engine. 
the last great improvement made by Mr. 
Watt, was his giving an impulse to the piston 
by the steam, both in descending and ascend- 
ing, instead of being impelled, as in the old 
engine, during the descent of the piston 
only. 
Having thus briefly 7 mentioned the prin- 
cipal improvements made in the steam-en- 
gine by Mr. Watt, we shall proceed to de- 
scribe one of his engines on the latest con- 
struction. 
A is the boiler, to which Mr. Watt has paid 
very great attention. It is generally of an 
oblong form; and the flame, after striking 
<>ii its concave bottom, circulates round the 
sides and sometimes returns in a pipe through 
the body ol the water before it is suffered to 
go up mto the chimney. In his engines 
t here are commonly two of these boilers, so 
that one of them may work while the other 
is repairing. B (Plate fig. 3) is the steam- 
pipe which conveys the steam to the cylinder 
( , which is cased, and closed at top by a 
plate, having a collar of leathers, through 
which the piston-rod D works, a and c are 
the steam-valves, through which the steam 
enters into the cylinder: it is admitted 
through a, when it is to press the piston 
downwards, and through c when it presses 
it Upwards, b and d are the eduction-valves, 
through which the steam passes from the cy- 
linder into the condenser e, which is a sepa- 
rate vessel placed in a cistern of cold water, 
and which has a jet of cold water continually 
playing up in the inside of it. f is the air- 
pump, which extracts the air and water 
from the condenser : it is worked by the 
great beam or lever ; and the water brought 
by it from the condenser, after being brought 
into the hot-well g, is pumped up again by 
the pump h, and is brought back again into 
the boiler by the pipe i. k is another pump, 
also worked by the engine itself, which sup- 
plies the cistern in which the condenser is 
placed, v\ ith cold water. 
In the old engines, where the working- 
stioke was only downwards, the piston-rod 
was attached to the beam by chains, which 
bent round an arch on the end of the beam, 
in order to make the piston-rod move always 
in a perpendicular direction. This may be 
seen in the plate of Newcomen’s engine. 
But in Mr. Watt’s engines, where the work- 
ing-stroke is doubled, that is, both upwards 
and downwards, chains could not answer 
this purpose, as, when the piston was forced 
upwards, they would slacken, and would not 
communicate the motion to the beam. It 
was necessary, therefore, that the piston- 
rod should be fastened to the beam by in- 
flexible bars ; but that the stroke might be 
perpendicular, a particular contrivance was 
invented by Mr. Watt, which is exhibited in 
the plate, and which answers the intended 
purpose admirably. It is usually called the 
parallel joint, and its nature and construction 
will be easily understood from the ligure. 
In order to make the engine itself open and 
shut the steam and eduction-valves, long 
levers are attached to them, which are moved 
by the piston-rod of the air-pump E E. T his 
part of the apparatus is called the working- 
geer, and is so contrived, that the valves may 
be worked either by hand or by the perpen- 
dicular rod. By shutting these valves, the 
engine may be stopped in an instant. 
In order to communicate a rotatory mo- 
tion to any machinery by the motion of the 
beam of the steam-engine, Mr. Watt makes 
use of a very large fly-wheel G ; on the axis 
ot which is a small concentric toothed wheel, 
H. A similar toothed wheel, 1, is fastened 
by straps to a rod coming from the end of 
tiie beam, so that it cannot turn round on its 
axis, but must rise and fall with the motion 
of the great beam. 
A bar of iron connects the centres of these 
two small toothed wheels, so that they can- 
not quit each other. When, therefore, the 
beam raises the wheel T, it must move round 
the circumference of the wheel H, and turn 
it together with the fly ; and it will be evi- 
dent, upon' consideration, that the fly, driven 
in tliis manner, will make two revolutions 
for every one of the wheel I. This mode of 
moving the flv, is preferable to a crank ; as 
it goes with twice the velocity. This con- 
trivance is called the sun and planet wheel, 
from the resemblance of the motion to that 
of those luminaries. 
The valves of this steam-engine are all 
puppet-valves, as these are found least liable 
to be out of order. 
The mode of operation in Mr. Watt’s en- 
gine, is as follows : 
Suppose the piston at the top of the cy- 
linder, in the situation represented in the 
plate, and the lower part of the cylinder filled 
with steam. By means of the handle E, open 
the steam-valve a, and the eduction-valve 
d, the levers of which are connected together ; 
there being now a ’communication between 
the cylinder and the condenser, the steam 
instantly rushes into the condenser, leaving 
the cylinder empty ; whilst at the same time 
the steam from the boiler, entering by the 
steam-valve a, presses upon the piston, and 
forces it down. As soon as the piston has 
arrived at the bottom, the steam-valve c, 
and the eduction-valve b, are opened, whilst 
the valves a and d are shut ; the steam there- 
fore immediately rushes through the educ- 
tion-valve b, into the condenser, whilst the 
piston is forced up again by the steam, -which 
is now admitted by the steam- valve c. 
Fig. 4, which is a section of the steam- 
pipes, taken at right angles to that in tig. 3, 
shews this more distinctly ; s is the pipe 
which conveys the steam from the boiler ; a 
and c are the steam- valves, and b and d the 
eduction-valves. By attending to the ope- 
ration in both the sections, the reader will 
easily understand it. It appears at first a 
little confused, by there seeming to be only 
one steam- pipe for communicating betwecu 
the cylinder and the condenser ; but the 
difficulty is cleared up, by representing both 
the pipes, as in tig. 4. 
Fig. 5, is a longitudinal section of the boil- 
er, representing the mode of supplying it 
with water, and the safety-valve and cocks, 
f is a small cistern, which is supplied with 
water from the hot-well, as represented in 
fig. 3 ; from the bottom of this cistern, a pipe 
goes down almost to the bottom of the boiler, 
where it turns up a little, to prevent the 
entrance of the steam which rises from the 
bottom. From the side of this cistern, is 
supported a small lever, to one end of which 
is fastened a wire, that carries a stone which 
hangs in the water of the boiler; the other 
end ot- the lever supporting also by a wire, 
a valve that shuts the top of the pipe that 
goes down from the cistern. Now, suppos- 
ing the stone just at the surface of the water, 
and balanced by a weight at the opposite 
end ot the lever ; it is evident, that by the 
laws ot hydrostatics, already explained, a 
certain part of the weight of the stone will be 
supported by the water, so long as it con- 
tinues immersed in it ; but if a part of the 
water evaporate by-boiling, a proportional 
part ot the stone will be above the water, 
consequently the stone w ill bear more upon 
the lever, and raise the weight at the other 
end ; but in raising that weight, it also opens 
the valve in the small cistern, and admits 
water until it stand at the same height in the 
boiler as before, and then the valve and the 
stone being again in equilibrio, the valve re- 
mains shut until a new quantity is evapo- 
rated. By this means the supply of water is 
very gradual, however, and not by tits and 
starts, as here described for the sake of illus- 
tration. 
It is found by experience, to be a much 
better method than a bail-cock, and the 
regular supplying of the boiler with water 
is of the first importance. As a check upon 
this, and to know perfectly the height of the 
water in the boiler, there are two cocks, g 
and h, one of which reaches nearly to the 
surface ot the water when at its prope* 
height, and the other enters a little below 
the surface. 
It is evident, that if the water be at the 
just height, and you open g, steam will 
issue ; and if h be opened, water will be driven 
out by the pressure of the steam. But 
if water come out from g, then the water 
must be too high in the boiler ; and if steam 
issue from h, then the water is too low 7 . By 
this means, it is easy to know at all times the 
exact height of the water m the boiler. 
i is a safety-valve, to prevent the bursting 
of the boiler by the steam growing too 
strong ; k is the pipe which conveys the steam 
to the engine. 
Fig, 6 is Mr. Cartwright’s steam-engine, 
the construction of which evinces much inge- 
